Centrifugal compressor

ABSTRACT

A multi-stage overhung centrifugal compressor having a split seal housing encompassing the impeller shaft that is vented directly to atmosphere. The seal rings contained within the housing are also split to permit the seal assembly to be mounted about the shaft without having to remove the shaft from its supporting structure.

United States Patent 1191 Robb et al.

1 51 Sept. 30, 1975 1 CENTRIFUGAL COMPRESSOR [75] Inventors: Raymond R. Robb, Latrobe; Donald C. Hewitt, Jeannette; Melvin G. Walter, .lr., Greensburg; Vijay K. Sood, Murrysville. all of Pa.

[73] Assignee: Carrier Corporation, Syracuse. N.Y.

[22] Filed: Sept. 5, 1974 [21] Appl. No.: 503,402

[52] U.S. Cl. 415/110; 415/170 A; 277/29; 277/75 [51] Int. Cl. FOID 11/00 [58] Field ofSeareh ..4l5/ll(). 111. 112, 170R. 415/170 A, 179; 277/29. 75, 154, 142., I99

156] References Cited UNITED STATES PATENTS 849.115 4/1907 France 277/75 980.594 l/l9ll Bulock 277/142 2.049.774 8/1936 Hoffman 415/1 70 A 3.035.808 4/1963 Williams 415/170 A 3.333.855 8/1967 Andresen... 277/142 3.680.973 8/1972 Pilarezyk.... 415/122 R 3.717.418 2/1973 Pilarezyk 415/179 3.748.065 7/1973 Pilarezyk 415/179 3.809.493 5/1974 Pilarezyk.... 415/122 R Prinmry Examiner-Henry F. Raduazo Attorney, Age/1!, or Firm-J. Raymond Curtin; Thomas J. Wall 5 7 ABSTRACT A multi-stage overhung centrifugal compressor having a split seal housing encompassing the impeller shaft that vented directly to atmosphere. The seal rings contained within the housing arealso split to permit the seal assembly to be mounted about the shaft without having to remove the shaft from its supporting structure.

5 Claims, 3 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of 3 3,909,154

U.S. Patent Sept. 30,1975 Sheet 2 of3 3,909,154

US. Patent Sept. 30,1975 Sheet 3 Of3 3,909,154

CENTRIFUGAL COMPRESSOR BACKGROUND OF THE INVENTION This invention relates to a centrifugal compressor and, in particular, to an overhung compressor having a modular configuration containing a split shaft seal that is ventable directly to the atmosphere.

More specifically, this invention relates to a split seal assembly suitable for use in an overhung compressor of the type wherein one or more interchangeable compressor sections are suspended from a stationary drive section, the compressor drive shaft being common to both the compressor sections and the drive section. Typically, in an overhung compressor assembly, the compressor sections are broken away from the ma chine drive along a vertical parting line that passes adjacent to or through the shaft seal assembly. It is also typical in this arrangement to employ sealing rings of one-piece construction which must be slipped over the end of the shaft during assembly or removal thereof.

Although the vertically split overhung construction is relatively simple, it nevertheless has certain disadvantages relating to the mounting of shaft seals that tends to offset the advantage of simplicity. First, because the machine is split in the vertical plane, the seals generally are buried well within the machine structure. Venting of the seal cavity, as normally required in a visco-seal arrangement or the like, becomes difficult. Because generous venting cannot be provided, special systems are needed to introduce artificial buffer air into the seal cavities, particularly during periods of startup or shut down. Buffer air systems have proven to be expensive, difficult to maintain. and often times unreliable. Secondly, in an overhung compressor using one-piece sealing rings, the compressor drive shaft must be removed from its support structure when the rings are to be mounted or removed from the machine. Accordingly, both the compressor section and the drive section of the machine have to be dismantled to gain access to the shaft in order to accomplish this task. This practice is also time consuming and expensive to perform.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve compressors and, in particular, overhung compressors.

It is a further object of the present invention to improve seal venting in an overhung compressor.

A still further object of the present invention is to faeilitate mounting and removal of shaft seals in a rotary machine without having to remove the shaft from the machine.

These and other objects of the present invention are attained in a rotary machine of the type wherein one or more compressor sections are suspended from a single drive section, the drive section including a stationary base and a removable cover being separable along a horizontal parting line. end plates secured to the base for suspending the compressor sections with the end plates extending upwardly adjacent to the cover to pro vide a generous air passage therebetwcen, a compressor drive shaft journaled for rotation within the drive section and being axially aligned with the horizontal parting line. the shaft passing into the compressor section through an opening in the drive section and the end plates, a split shaft seal assembly insertable between the end plate and the drive section having at least two split rings mounted therein for encompassing the shaft to form a vent cavity therebetween, and venting means for placing the vent cavity in fluid flow communication with the air passage formed between the end plate and the cover.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. I is a side view of a rotary machine embodying the teachings of the present invention,

FIG. 2 is an enlarged partial view in section of the machine illustrated in FIG. 1 showing a split seal housing positioned between the end plate and the drive section, and

FIG. 3 is a section taken along line 3-3 in FIG. 2 further showing the construction of the split seal housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 depicts an overhung compressor, generally referenced 10, which includes a support stand 11 upon which is mounted an electrical drive motor 12. The motor is operatively connected to a main machine drive section 13 via a shaft 14. A series of compressor sections l5, 16 are suspended from the drive section upon vertically extending end plates 17, 18. The drive section of the machine is of two-piece construction consisting of a stationary base 19 secured to the stand and a removable cover 20 affixed thereto by means of bolting flanges 21, 22. As illustrated, the cover is separable from the base along a horizontal parting line 23. Although not shown, a bull gear, operatively connected to drive shaft 14, is rotatably supported within the drive section and, as will be explained below, translates power from the motor to the compressor sections hung upon the drive section.

As more clearly seen in FIG. 2, a horizontally aligned pinion shaft 25 is also rotatably supported upon bearings, as for example bearing 26, within the drive section 13 of the machine. In practice, the shaft is axially aligned with motor shaft 14 and the horizontal parting line 23 of the drive section so that access to the shaft is gained when the cover is removed from assembly. FIG. 2 illustrates the left-hand end of the pinion shaft as seen in FIG. 1, passing through shaft opening 28 formed in the drive section and the left-hand end plate 17 into compressor section 15. It should be understood that the opposite end of the shaft passes into compressor section 16 and is similarly supported in the righthand side of the drive section and the right-hand end plate 18. For explanatory purposes, however, the shaft mounting arrangement will only be described in reference to the right-hand end of the shaft.

Shaft 25 extends into the compressor section 15 and has affixed thereto an axially aligned stud 30 upon which is mounted a first stage impeller 31. The machine herein disclosed embodies a modular concept wherein the compressor stages are all fabricated of standard parts that are capable of being suspended from the end plates in a variety of different arrangements. As more fully disclosed in co-pending U.S. application Ser. No. 503,401, filed Sept. 5, 1974, the disclosure of which is herein incorporated by reference, the impellers of the various compressor stages are removably affixed to either end of the pinion shaft and can be conveniently mounted in different numbers and orders to accommodate the various modular configurations. An important aspect of this modular approach resides in the fact that the compressor shaft or shafts supported in the drive housing do not have to be removed from their supports when the machine configuration is altered to accommodate different flow ranges.

The machine illustrated in FIG. I, basically is a threestage compressor having the first stage impeller housed in compressor section and the second and third stage impellers housed in compressor section 16. It should be clear, however, that this particular arrangement of compressor components can be changed and more than a single shaft can be similarly mounted in the drive section to accommodate further stages. In practice, the working fluid to be compressed enters the first stage of the machine by means of inlet 34 (FIG. 1) and after compression is discharged into an intercooler (not shown) mounted in the stand 11 via discharge piping 35. After cooling, the fluid enters the second stage through piping 36, passes through the second and third stages of compression, and is finally discharged from the compressor via discharge piping 37.

The lower base 19 of the drive section 13 is provided with a pair of semicircular bosses 40, 41 to which are secured the end plates 17 and 18, respectively, for example by bolting or welding. The end plates are supported in a substantially vertical condition with the upper half of each plate being freely suspended adjacent to the cover thus establishing an air passage 43 therebetween extending downwardly, deep into the machine structure.

Referring once again to FIG. 2, a split seal assembly 50 is positioned outboard of the bearings within the shaft opening 28 containing a pair of split sealing rings 53 which encompass the shaft to form an annular vent cavity 54 thercbetween. The rings are supported within a cylindrical housing 55 that is split into two equal halves 55((1) and 55(1)) as best seen in FIG. 3. In assem bly, the split seal housing is mounted between the end plates and the drive section directly below the air passage 43. A vertical air channel 56 is machined in hub 57 of the cover which extends the air passage direetly into the shaft opening above the seal housing. The vent cavity 54, formed between the rings, is placed in fluid flow communication with the channel, and thus the air passage, by means of a series of radially extended openings 58 that empty into an annular chamber 60 formed in the outer periphery of the housing. As can be seen, the annular chamber discharges directly into the channel whereby fluids are efficiently ex changed between the vent cavity and atmosphere.

Normally, in this type of shaft seal arrangement, the sealing rings are preferably formed of carbon and are supported with a minimum ofclearance about the shaft to reduce leakage thercbetween. The rings thus prevent high pressure fluids processed in the compressor from passing into the drive section and oil and oil vapors contained in the drive section from moving into the compressor section. Because some leakage occurs over the rings, it is essential to vent this leakage out of the system. For example, during startup or shutdown of the machine, there is generally a loss of pressure experienced in the compressor sections whereby a negative pressure is felt on the compressor side of the seal assembly. Without generous venting of the seal cavity, oil or oil vapors can be pulled from the drive section into the compressor section. Conventionally, in a vertically split machine, where the seals are buried within the structure, sufficient venting cannot be achieved to prevent an oil crossover and artificial buffer air must be introduced into the cavity. Buffer air systems have proven to be expensive, relatively bulky, and often times unreliable.

The apparatus of the present invention avoids these problems by providing generous natural venting of the seal cavity. During startup or shutdown, air is readily drawn into the vent cavity to provide a buffer between the compressor and drive sections. By the same token, under normal operating conditions, when high pressures are generated in the compressor section, this pressure is broken down over the sealing rings and any leakage into the vent cavity is quickly passed to atmosphere rather than into the drive section where it can cause misting.

Referring once again to FIGS. 2 and 3, the sealing rings are supported within recesses formed within the internal opening of housing 50. The rings are springbiased axially against one radial wall of the recess and also radially towards the shaft. The sealing rings can be formed of two or four coacting segments equally contained within each half of the housing. Although not clear from the drawing, sufficient clearance is provided to permit each half of the housing to be slipped over the shaft when the drive cover is removed. The two halves of the housing are then pinned together by dowels 65 (FIG. 3) and then bolted together via cap screws 66. In assembly, the ring segments are supported in alignment against one wall of the recess and the end face brought into contact under the influence of the springs. so that a continuous sealing surface is presented to the shaft having a minimum amount of clearance thercbetween.

To prevent rotation of the seal housing in assembly, a pin is staked to the seal housing. The pin extends outwardly from the outer periphery of the housing and is received in a groove 71 machined in the end face of plates 17, 18. Axial shifting of the housing is also prevented by a pair of arcuate-shaped retaining rings 74,

75 which are insertable into a complementary slot that is coextensively formed in the seal housing and the drive housing so that approximately one-half of the surface area of each ring engages each of the contiguous members. An O-ring seal 77 is also mounted in a groove formed about the outer periphery of the seal housing with the O-ring being arranged to seat in sealing contact against the surface of the shaft opening thus preventing the working fluids from moving thercbetween.

As can be seen, the present shaft sealing arrangement is extremely well suited for use in an overhung compressor environment wherein a drive section is split horizontally along the center line of the impeller drive shaft. The shaft seal housing is permitted to extend between the drive housing and the end plate supporting the compressor section whereby a generous venting passage to atmosphere can be established within the seal region thus avoiding many of the problems associated with more conventional seals ordinarily buried deep within the machine structure. Furthermore, because of the present construction, the seal housing and seals can be conveniently mounted or removed in respect to the drive shaft without having to remove the shaft from assembly or decoupling the shaft from the drive system. V

While this invention has been described with reference to the structure herein disclosed, it is not confined to the details as set forth, and this application is intended to cover any modifications or changes that may come within the scope of the following claims.

What we claim is:

1. In a compressor,

a drive assembly including a base and a removable cover being separable-along a generally horizontal parting line, the drive section containing a driving member,

an end plate secured to the base and extending upwardly adjacent to the cover to establish an air passage therebetween,

a compressor casing suspended from the end plate containing a compressor rotor,

a pinion shaft for driving the compressor rotor operatively connected to the driving member, said shaft being rotatably supported within the drive section and extending through a shaft opening formed in said drive assembly and said end plate into the compressor casing,

a seal housing axially split into two sections being mountable about said shaft within said opening with one end of the housing being seated within said end plate and the opposite end of said housing being seated within said drive assembly,

a plurality of radially aligned axially split sealing rings mounted within said housing for encompassing said shaft for forming a vent cavity therebetween beneath said air passage, and

venting means for placing the vent cavity in fluid flow communication with said air passage and means for retaining said vent cavity and said air passage in communication.

2. The compressor of claim 1 having further means for securing said housing in said shaft opening to prevent axial and rotational movement thereof.

3. The compressor of claim 1 wherein said housing includes an annular chamber formed in the outer periphery thereof arranged to discharge directly into said air passage and a series of radial openings passing between said chamber and the vent cavity.

4. The compressor of claim 1 further including a seal positioned between the end plate and the housing for preventing fluids from moving therebetween.

5. The compressor of claim 1 wherein the two sections are insertable about the shaft when said cover is removed from said drive assembly. 

1. In a compressor, a drive assembly including a base and a removable cover being separable along a generally horizontal parting line, the drive section containing a driving member, an end plate secured to the base and extending upwardly adjacent to the cover to establish an air passage therebetween, a compressor casing suspended from the end plate containing a compressor rotor, a pinion shaft for driving the compressor rotor operatively connected to the driving member, said shaft being rotatably supported within the drive section and extending through a shaft opening formed in said drive assembly and said end plate into the compressor casing, a seal housing axially split into two sections being mountable about said shaft within said opEning with one end of the housing being seated within said end plate and the opposite end of said housing being seated within said drive assembly, a plurality of radially aligned axially split sealing rings mounted within said housing for encompassing said shaft for forming a vent cavity therebetween beneath said air passage, and venting means for placing the vent cavity in fluid flow communication with said air passage and means for retaining said vent cavity and said air passage in communication.
 2. The compressor of claim 1 having further means for securing said housing in said shaft opening to prevent axial and rotational movement thereof.
 3. The compressor of claim 1 wherein said housing includes an annular chamber formed in the outer periphery thereof arranged to discharge directly into said air passage and a series of radial openings passing between said chamber and the vent cavity.
 4. The compressor of claim 1 further including a seal positioned between the end plate and the housing for preventing fluids from moving therebetween.
 5. The compressor of claim 1 wherein the two sections are insertable about the shaft when said cover is removed from said drive assembly. 